5080 Error on Transaction

Hello I am having issues with my gravity forms and the transaction failing with a 5080 error.
I have seen other threads in your support, (I did comment there but forum masters deleted my post as it was an old thread?) I have made sure that the currency is GBP and have looked in the sage account to see if it expands on the error but Sage does not even register the transactions – it is almost like it fails before getting through to Sage.
Looking through the Sage forums it says that a 5080 error could be an issue with encryption.

In certain circumstances the transaction will not show up in this screen, indicating a problem with the encryption used on your post.

This has been working on the site for well over a year with no problems but a few days ago it just stopped working. Have you any ideas of what is causing the issue?

Below is a copy of the debug from your plugin – unfortunately it doesn’t mean much to me:

2017-10-04 15:34:51.785710 - DEBUG --> GFFeedAddOn::maybe_process_feed(): Marking entry #4585 as fulfilled for gravityforms-sagepay-form 
2017-10-04 15:34:51.995661 - DEBUG --> Sending to SagePay Form: {pre>Array
(
    [VPSProtocol] => 3.00
    [TxType] => PAYMENT
    [Vendor] => VENDORNAMEWAS HERE
    [Crypt] => @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
)
/pre>} 
2017-10-04 15:34:56.738662 - DEBUG --> GFPaymentAddOn::maybe_process_callback(): Initializing callback processing for: gravityforms-sagepay-form 

All plugins on the site are at the latest version, any help would be greatly appreciated.

The page I need help with: [log in to see the link]